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Outline 6
Comparative Physiology- Renner Lecture 6
Question | Answer |
---|---|
The nervous system provides means of ________ ___________ between an ______ and the _______ and _______ environment | rapid communication, organism, external, internal |
what are the three components of the nervous system ? | receptors, neurons, effectors |
what are receptors? give an example | sense organs- ex: rods in retina are specialized photoreceptors, only light/dark vision. |
what are neurons? | modified epithelial cells that integrate information and are specialized to conduct impulse through specialized excitable membrane to an effector aka motor neuron. |
what are effectors? give some examples | effect or act on the stimulus in the form of an action. an example is a muscle or an endocrine gland. |
single celled organisms (amoeba) and simple multicellular organisms (Phylum Porifera) can respond to stimuli but are not considered nerve cells, why? | Because reception of a stimuli, conduction, and effector, are all in one unit. Cell to cell transmission is slow in sponges, and they contain no neurons. |
the first evidence of the receptor/conduction function from the effector appears in the _____________________ | Phylum Coelenterata |
Phylum Coelenterata have specialized cells of ________ origin arranged in a ________________ | ectodermal, nerve net |
what two major advances that improve the efficiency of the nervous system in higher organisms? | 1. cephalization/concentration of sensory organs, receptors in the head region; presence of ganglia (aggregates of neurons) help actively process info. 2. separation of nerve functions into sensory and motor components; result in reflex arc. |
Explain what a reflex arc is and why it is useful | Sensory neurons that receive input from a receptor, transfer that input to a motor neuron which then activates an effector. It does not include in the brain. |
what is the advantage of the addition of interneurons in vertebrates and higher invertebrates to the reflex arc ? | it allows the stimulus to be passed on to to multiple effectors |
the nervous system of vertebrates contains two classes of neurons what are they? | Neurons and neuroglia |
if depolarization reaches ___________ it will trigger a/an_________________ | threshold, action potential |
axon hillock is a region of ____________ | integration |
The axon is the ___________ portion of the neuron, while dendrites are ______________ units | transmitting, receiving |
axons generally terminate as a branched structure; branches known as ____________ also emerge from the axon | collaterals |
What are the general types of neurons? | Unipolar, Pseudounipolar, Bipolar, Multipolar |
Describe a unipolar neuron, where are they found? | It has one process that gives rise to branches. Commonly found in invertebrates, they are present in vertebrates during embryological development. Found in ganglia of adult mammals' autonomic system. |
Describe a pseudounipolar neuron, where are they found? | initially develop as bipolar but the dendrites and axon fuse during development to form a single process coming out of the soma. Function as sensory neurons in spinal ganglia. Not present in invertebrates since they do not have a spinal cord. |
Describe a bipolar neuron, where are they found? | It has a single axon and a single dendrite emerging from the soma. Found in retina, and olfactory epithelium. |
Describe a multipolar neuron, where are they found? | It has a single axon and multiple dendrites. It is the most common type found in vertebrate nervous system. Ex: Purkinjee cell- 150,000 dendritic branches |
What are the 5 types of neuroglia? | 1. oligodendrocytes 2. schwann cells 3. astrocytes 4. microglia 5. ependymal cells |
These neuroglia cells form myelin sheath on axons in the CNS | Oligodendrocytes |
These neuroglia cells form myelin sheath in the PNS | Schwann cells |
These neuroglia cells maintain ion balance, degrade neurotransmitters, synthesize neurotransmitters. | Astrocytes |
This type of neuroglia cells are associated with white matter axon tracks | Fibrous astrocytes |
These neuroglia cells are phagocytic, they are derived from microphages. | Microglia |
These neuroglia cells line ventricles of brain, choroid plexus, and secrete CSF | Ependymal cells |
in which membrane is membrane potential altered and for what purpose? | in excitable membranes, it is to allow signal transmission |
the action potential is a _________ event | membrane |
what is meant by depolarization? how does that affect AP? | it means that the inside of the cell becomes less negative. When threshold is reached, an AP will be initiated. |
Define threshold | critical level of depolarization, makes polarity of membrane positive. When reached the AP will occur. |
TRUE OR FALSE: The change in membrane potential during AP is long lasting | FALSE. It is short lasting |
An AP is initiated in an _____________ fashion | all or none |
TRUE OR FALSE: The amplitude of an AP can be increased by increasing the duration or intensity of the stimulus | FALSE. it cannot be increased like that |
what is a refractory period? | period where a second stimulus will not initiate an action potential |
What event drives the membrane potential closer to threshold? | The opening of VgNa+ channel that open as a result of depolarization due to stimulus |
What value is the membrane potential driven to at the start of an AP? | The membrane potential is driven towards the equilibrium potential of Na+ which is +55mV |
VgK+ channels in the membrane also open after a ____________ period | lag |
what two events lead to increased efflux of K+ compared to K+ influx? | The opening of VgK+ channels and the inactivation of VgNa+ channels after a brief period of time |
what potential is the membrane driven back to? | It is driven back to -80mV, the equilibrium potential of K+ |
What event contributes to the hyperpolarization of the membrane? | VgK+ channels staying open for a brief period of time |
how are the chemical gradients across the membrane restored? | Via Na+/K+ pump |